Method for manufacturing carpet having low static charge

ABSTRACT

A METHOD OF PRODUCING CARPET OF LOW STATIC CHARGE, WHEREIN A BINDER CONTAINING THEREIN A QUANTITY OF CARBON FIBER IS APPLIED TO THE BASE CLOTH FOR THE CARPET AS WELL AS TO THE FLOCKED FIBERS.

United States Patent US. Cl. 117-139.5 C 3 Claims ABSTRACT OF THEDISCLOSURE A method of producing carpet of low static charge, wherein abinder containing therein a quantity of carbon fiber is applied to thebase cloth for the carpet as well as to the flocked fibers.

This invention relates to manufacture of carpet having very low staticcharging, and, more particularly, to an improved method of antistaticprocessing of the carpet.

Known type of carpet is mostly manufactured from woven cloth of hemp orcotton yarn as the base, into which other fibrous material such as wool,polyester, nylon, etc. are enmeshed so as to be flocked thereinto. Also,in most cases, a rubbery material is coated on or impregnated in thebase cloth as a binder with a view to securing adhesion between the basecloth and the flocking.

Since these fibrous materials are insulative, static electricity tendsto generate. Therefore, the carpet is not only charged with staticelectricity, but it tends to cause static charging of an oppositepotential against an object which contacts therewith such as livingbodies, etc. This static charging often imparts to such living body ashock at the time of electric discharge, or, where there is inflammablegas or liquid, explosion or fire is inevitably caused. In recent days,synthetic fibers are used widely in various purposes such as for carpet,clothing, rfurnitures and fittings, and so forth with the consequentincrease in the abovementioned phenomenon, which tends to becomeunavoidably remarkable in the dry season.

Heretofore, it has been attempted to prevent static charging by mixing asmall quantity of metallic fibers such as stainless steel with fibersfor weaving the base cloth or for flocking so as to make the productelectroconductive. This attempt resulted in the antistatic effect to acertain degree. However, not only was it difficult to manufactureuniformly interwoven base cloth, but also, when a mixing quantity of themetallic fiber is increased with a View to attaining sufficient effect,outer appearance of the product is impaired. Also, fine stainless steelfiber is extremely expensive, which is another cause for preventing thematerial from practical use.

It is therefore an object of the present invention to provide a methodfor manufacturing carpet or like articles free from static charge, themethod of which is simply attained by mixing quantity ofelectroconductive carbon fibers with a binding material to be appliedonto the carpet.

The above object and other objects of the present invention will becomemore apparent from the following description along with a few preferredexamples thereof.

As the characteristic point of the present invention is to mix carbonfibers with rubbery or plastic material as a binder, outer appearance ofthe flocked fibers is not impaired, because the carbon fiber does notappear on the flocked surface. Hence, it is possible to manufacturecarpet in exactly same manner as in the ordinary carpet production.

Wee

It is really surprising that static charging in the overall carpet isprevented by simply mixing carbon fibers with insulative rubber orplastic material as a binder. This antistatic phenomenon due to carbonfiber is assumed to be that static electricity generated at a portion ofthe flocked surface is spread widely thereover on account of the carbonfibers existing in the binder, and is discharged therethrough into airor ground.

Carbon fibers to be used in the present invention designate generallycarbonaceous or graphitic fiber of electroconductive property. Diameterof a carbon monofilament usually ranges from about 3 microns to about 30microns, and its length ranges in average between 0.5 mm. and 10 mm.Over 10 mm. of the fiber length, it becomes difficult to uniformlydisperse the carbon fiber in the binder by kneading, and to cause thecarbon-fiber-containing binder to be uniformly coated on or impregnatedin the base cloth. Less than 0.5 mm. of the fiber length,electroconductive effect in the product becomes low.

Adding quantity of carbon fiber to the binder should preferably be from0.1 to 10.0% by weight with respect to parts by weight of the solidcontent of the binding material. Quantity of less than 0.1% by weight ofthe carbon fiber would not produce the electroconductivity in the binderto a suflicient degree. Excessive quantity over 10.0% by weight resultsin diificulty in coating or impregnating operation. The adding quantityis in any way determined in relation to the fiber length.

As the carbon fiber has its specific gravity of about 1.5 to 1.9, and issmaller than that of stainless steel fiber by a few fractions, itsvolume becomes several times as large as that of stainless steel fiberfor the same weight, hence the desired effect of electroconductivity canbe easily exhibited.

It has so far between known to add carbon black to impartelectroconductivity to rubbery material. However, as the carbon black isin very fine powder, the intended object cannot be achieved withaddition of a small quantity thereof. Usually, 10 to. 35% by weight ofcarbon black is added to the binder material. From this comparison, itcan be understood that the use of carbon fiber brings an advantageousresult to the product.

Material for the binder may be those available in the market such asnatural rubber, butadiene-styrene rubber (SBR), butadiene-acrylonitrilerubber (NBR), polyvinyl chloride (PVC), polyethylene, polyurethane, andso on.

Mixing of the carbon fiber with these binding materials is carried outby an ordinary method such as roll-kneading, solvent dispersion, etc.Any known method may likewise be adopted in accordance with actualsituation. Same can be said of coating or impregnating the base of clothwith the binder.

According to the method of the present invention, it is possible thatthe antistatic effect may be suificiently exhibited by adding apredetermined quantity of electroconductive carbon fiber to the bindingmaterial alone, so that any complicated process such as mixing orinterweaving the carbon fiber with the flocking fiber or the base clothis no longer necessary. Further, the carbon fiber, once mixed with thebinding material, is no longer required to be subjected to bendingaction due to external force, against which the carbon fiber is mostfragile, hence the resultant article of manufacture is durable enoughagainst external force and has wide varieties of use.

In order to enable skilled persons in the art to readily reduce thepresent invention into practice, the following actual examples arepresented. It should however be noted that these examples areillustrative only and do not intend to narrow the scope of protection asrecited in the appended claims.

3 EXAMPLE 1 Carpet was manufactured from a woven base cloth of hemp yarnand nylon pile having the fiber length of 6 mm. when flocked. The backsurface of the base cloth was coated with liquid butadiene-styrenerubber. The rubber material used was a product of Yokohama Rubber (30.,Japan, and identified as No. Y-460."

Carbon fibers of an average length of about 3 mm. and a diameter ofabout 7 microns was mixed with the liquid rubber component at the mixingratios of 0.5% by Weight and 2.0% by weight, respectively, with respectto the solid rubber content. The quantity of the rubber componentapplied to the base cloth was 150 g./m. and 3,600 g./m. for therespective test pieces of diiferent carbon fiber contents.

From the carpets thus manufactured, test pieces of 3 cm. x 4 cm. werecut out. The specimens were subjected to test for measuring the chargedvalue of static electricity by means of a rotary static tester (producedby Koa Shokai Co., Japan). The test results are shown in Table 1 below,from which remarkable antistatic effect is recognized with the bindercontaining the carbon fiber.

friction in the same manner as in Example 1 above. The results are shownin the following Table 3.

EXAMPLE 4 Carbon fiber of about 12 microns in diameter and about 3 mm.in average length was added to liquid SBR No. Y-460 (product of YokohamaRubber (30., Japan) at a ratio of 0.3% by Weight with respect to thesolid rubber content to prepare a binder. This binder was applied ontocarpet made of base hemp cloth and woolen pile having fiber length of 6mm. in a quantity of 500 g./m. and then the carpet was dried.

From the thus produced carpet, a test piece of cm. x 30 cm. was cut out,and dried at a temperature range of from 100 to 110 C. for 2 hours.After drying, the test TABLE 1 Quantity of binlde Static voltage (v.)after friction forapp 1e Binder (g./m. 10 sec. 20 sec. 30 sec. 60 sec.120 sec.

Specimen number:

1 SBR 150 1, 450 1, 700 1, 800 1, 900 2, 000 R 3, 600 1, 450 1, 600 1,700 1, 750 1, 750 150 700 850 950 1, 100 1, 300 -dO 3, 600 400 500 600680 750 SBR plus 2.0 wt. percent carbon fiber. 150 200 500 600 800 1,050.do 3, 600 200 500 550 600 800 N orE.Rotary Static Tester used in thisexample is an apparatus for measuring static electricity charged byfriction between the test pieces and friction cloth. The test piece isfitted on the outer surface of a cylinder 01 this apparatus, and, whilethe cylinder is in rotation, the test piece is in contact-motion withthe tnctmn cloth placed in opposite side of the cylinder. Themeasurement was conducted in a chamber of 26 C. and 65% of relativehumidity.

EXAMPLE 2 300 g./m. of SBR binder was coated on carpet produced fromwoven base cloth of cotton yarn and woolen pile of 6 mm. fiber length.

For comparisons sake, following three kinds of the binder were prepared:(1) SBR alone; (2) SBR 5 Wt. percent of stainless steel fiber of about 7microns in diameter and about 5 mm. in average length; and (3) SBR 5 wt.percent of carbon fiber of about 7 microns in diameter and 5 mm. inaverage length.

In the same manner as in Example 1, static electricity was measured, theresults of which are shown in the folpiece was placed on a board of 5mm. thick made of polyvinyl chloride, on which there stood a human beingof 170 cm. tall, 60 kg. of weight, who wore cotton undershirt andfatigue cloth thereover, put a rubber-sole footwear on, and held in handan iron plate of 30 cm. x 30 cm. x 5 mm. After making several steppingson this test piece, static charge was measured for each of the ironplate in hand and the carpet. The results are shown in Table 4 below.

For the sake of comparison, same measurement was carried out on bothordinary carpet and a carpet made of the base cloth, in which stainlesssteel monofilament of 8 microns in diameter was interwoven with the hempyarn lowing Table 2. at a rate of 0.3% by weight with respect to thehemp TABLE 2 Static voltage (v.) after friction for- Specimen numberBinder 20 sec. 30 sec. sec. 120 sec 1 SBR (Y-460) 500 740 1, 180 1, 4302. SBR (Y-460) plus 5 wt. percent stainless steel fiber 370 550 700 7003 SBR (Y-460) plus 5 wt. percent carbon fiber 70 80 170 400 EXAMPLE 3 Toviscous liquid of natural rubber dissolved into carbon tetrachloride,carbon fiber of about 7 microns in diameter and about 0.1 mm. in averagelength was added so as to be a content of 0.1% by weight with respect tosolid rubber content.

The binder was impregnated in carpets made of a base hemp cloth andnylon piles having fiber length of 3 mm. and 6 mm., respectively, sothat the final quantity of the binder as applied to the respectivecarpets may be 500 g./m. and then the carpet was dried. Another carpetfor comparison purpose was also manufactured in the same manner, exceptthat no carbon fiber was added to the binder. Test pieces were takenfrom each of these caryarn, and woolen pile, in which the same metallicfilament is enmeshed in the same amount as the base cloth. It was foundthat the static charging in the carpet according to the presentinvention was very small.

Living body (iron plate) -1, 500

What we claim: 1. A method for preventing static charge in a pile carpetpets and tested for the static voltage after 60 seconds which comprisesbinding the base cloth for the carpet and pile with a binder selectedfrom the group consisting of natural rubber, butadiene-styrene rubber,butadieneacrylonitrile rubber, polyvinyl chloride, polyethylene andpolyurethane, containing therein a uniform dispersion of 0.1-10% byweight of carbon fibers having a single fiber length of 05-10 mm. and adiameter of 3-30 microns, based on the weight of the solid content ofthe binder, and drying the treated carpet.

2. The method as claimed in claim 1, in which the dispersion of binderand fiber is applied to the base cloth by coating.

3. The method as claimed in claim 4, in which the dispersion of binderand fiber is applied to the base cloth by impregnating.

References Cited UNITED STATES PATENTS 2,302,003 11/1942 Cadwell et al161-66 3,166,465 1/1965 Rahmes 161-66 3,235,323 2/1966 Peters 8116.23,486,920 12/1969 Sington 161-66 X WILLIAM D. MARTIN, Primary Examiner10 T. G. DAVIS, Assistant Examiner U.S. C1. X.R.

11713'8.8 F, 138.8 N, 161 UD, 161 UP, 161 KP, 162, 226

